Systems are well known to allow access to broadcasted contents such as Pay-TV events. In brief, these systems function by means of a multimedia unit including an MPEG descrambler. The MPEG descrambler receives the contents and is responsible for analogically reproducing said contents, in particular through audio and video signals.
These systems that allow access to subscription or Pay-TV television contents are currently being developed. These systems use the Internet network and xDSL (Digital Subscriber Line) type lines and in particular ADSL (Asymmetric Digital Subscriber Line) type lines to provide subscribers with broadcasted contents.
In systems of this type, contents that can be a television channel, an event such as a film or in particular a sports match, a music file or other similar contents are emitted in the form of a stream by a diffusion centre. The contents are transmitted by means of a satellite, terrestrial link or cable connection or by a combination of these different means to a retransmission centre that is responsible for diffusing the data forming this content intended for the multimedia units concerned. In order to allow this diffusion, the retransmission centre comprises a routing device that is responsible for the routing of the data to the multimedia unit for which the data is intended. This type of routing device is known under the acronym DSLAM (Digital Subscriber Line Access Multiplexer).
In this type of current system, the users wishing to gain access to content proposed by a content provider must generally subscribe with this supplier. In this case, all the contents managed by this provider are accessible to the subscriber. In fact, it is considered that the identification of a user by his/her telephone line is sufficient to provide said user with access rights to these contents.
This means that audio/video contents are transmitted in plaintext between the routing device (DSLAM) and a subscriber. This situation has opened the way to abuses such as those known under the name “Address spoofing”. Address Spoofing or IP Spoofing, consists in passing oneself off as someone else, by using his/her address on the network. In this way it is possible to make the provider believe that the connection or the transmission request for contents originates from an authorized user account.
A first solution to this problem has been proposed in the document WO2004/010698 that consists of encrypting the contents transmitted in a specific way. This document relates to the personalization of contents using specific control words. The transport medium is not affected by personalization operations.